Active harmonic filters: Evolution from classical to advanced engineering practices - A comprehensive review

The rapid growth of power-electronic converters has elevated harmonic mitigation from a secondary power-quality concern to a core requirement for grid compliance, reliable operation, and stability. Passive filters remain attractive for their simplicity and low cost, but suffer from detuning, resonance, and poor adaptability under varying conditions. Active harmonic filters (AHFs) use controlled converters to deliver adaptive, broadband compensation suited to converter-dominated grids. This paper reviews active harmonic filtering from a system-level perspective, covering shunt, series, hybrid, and unified configurations; two-level, multilevel, and modular converters; and resonant, predictive, nonlinear, and data-driven control. It treats DC-link energy, thermal stress, grid interaction, and component aging as first-order constraints rather than secondary concerns. Particular attention is given to high-power applications—most notably fast electric-vehicle (EV) charging— where compensation capability may be constrained by thermal and energy headroom, semiconductor current rating, modulation-voltage margin, DC-link ripple, and other operating limits. Performance metrics, benchmarking, and validation practices are consolidated into an AHF Minimum Reporting Set that extends comparison beyond total harmonic distortion (THD) alone; the limits of simulation-only studies are highlighted. Open challenges include weak-grid operation, wide-bandgap reliability, coordinated multi-converter control, and intelligent reliability-aware AHFs.